1. Field of the Invention
This invention relates to a rotary developer used in the formation of vias in dielectric layers made of photohardenable polymer for hybrid microelectronic parts and, more particularly, to a developer that provides uniform development of part layers and vias.
2. Description of the Prior Art
Photohardenable polymers used in the formation of dielectric layers for hybrid microelectronic parts have traditionally been difficult to develop. These electronic parts can comprise a ceramic substrate with a layer of a conductive material, such as copper, on one side of the substrate and a photohardenable layer on the conductive material. The photohardenable layer comprises a layer of photohardenable polymer, which may be a photosensitive composition which upon exposure to actinic radiation forms crosslinks or polymers of higher molecular weight changing the rheological character of the compositions. Preferably the layer is a thermoplastic layer. The photohardenable layer is exposed to actinic radiation through radiation transmissive areas of a radiation blocking mask. The radiation blocking areas of the mask leave unhardened portions in the shape of vias extending from a front surface of the layer to the conductive material. The polymer layer is developed by removing or washing away the unhardened portions with an appropriate liquid to form the vias. When the photohardenable polymer is Fodel.RTM., the liquid can be a solvent, such as 1,1,1-trichloroethane and unexposed portions are dissolved in the liquid and washed away. The layer including its walls defining the vias are then dried. The vias can be filled with conductive material, such as copper or gold to provide a conductive path between the layer of conductive material and an integrated circuit (IC) chip to be mounted on the dielectric layer.
U.S. Pat. No. 3,772,104 discloses a prior art spinning developer. The developer comprises a disk rotated by a motor. The electronic part is attached to the disk. An etching solution is sprayed at the part while the part is spinning with the rotor. The soluble portion of the photoresist is removed as a result of the impact(s) of the solution on the photoresist and the gravity and centrifugal force acting on the solution containing the dissolved or removed photoresist on the spinning part.
A spinning developer, like the one just described, has been used to remove unexposed photopolymer portions of a layer on an electronic part. In this developer, the nozzle spraying the solution at the part is located generally on a line perpendicular to the part with the line spaced from the part axis of rotation. See FIG. 1 which illustrates such a part 10 rotating in the counterclockwise direction as indicated by the arrow A. The nozzle is centered on a line intersecting and directed toward point P. The nozzle is a conventional fan spray nozzle which sprays an atomizing mist generally in a continuous planar fanning out pattern along the line L.
The above described developers have low productivity because only one part can be processed on each machine at a time. Required high spin rates, typically around 3,000 revolutions per minute (rpm), also limit use of these developers to parts which are symmetrical about a spin axis to avoid high forces during spinning which might cause the part to fly off the machine. A further limitation is the problem of uniformly developing parts, especially large parts, because of the different spray treatment received by a part from the spin axis out to the periphery of the part.
It is an object of this invention to provide a rotary developer that processes more than one electronic part at a time.
It is another object of this invention to provide a rotary developer that uniformly develops parts including large parts and nonsymetrical parts.